Polysulfones are commercially available thermoplastics which are widely used in a variety of applications such as adhesives, composites, or moldings for use in automobiles, household appliances and other applications. As thermoplastics, they are generally amorphous and creep under load at elevated temperatures. A more important use limitation is their sensitivity to various solvents, especially when the polymer is in a stressed condition. Because of this solvent sensitivity, conventional polysulfones cannot be used in many applications such as adhesives or composite matrices for use on commercial airplanes, which may be exposed to numerous solvents such as hydraulic and deicing fluids, fuel, and paint strippers. Composites from polysulfones, especially under load, exhibit pronounced crazing and cracking upon exposure to solvents, with loss of mechanical properties.
Various routes have been employed in an attempt to overcome the two major use limitations of polysulfones, creep at elevated temperature and solvent sensitivity. Each such attempt has not been entirely successful because either new difficulties were introduced or the original problem was not entirely solved. In one such application, polysulfones containing crystalline regions which serve as cross-links were employed to increase solvent resistance. The problem with using crystallinity to attain solvent resistance is that the material is more difficult to process and the physical properties of the polymer depend upon the amount or degree of crystallinity which is introduced into the polymer. The degree to which the polymer crystallizes is difficult to control and maintain, and when the degree of crystallinity changes, the physical properties change accordingly. This makes polymers of this type undesirable in certain applications, as in the design of airplane components which must be capable of performing for more than 50,000 hours in hostile environments.
An ethynyl-terminated sulfone monomer has been previously prepared and thermally polymerized to yield a brittle resin (elongation of approximately 6%) (see M. G. Maximovich, S. C. Lockerby, F. E. Arnold, and G. A. Loughran, Science of Advanced Material and Process Engineering Series, vol. 23, p. 490 (1978)). The present invention differs from this in that higher molecular weight materials are used to retain toughness and the chemistry involved is entirely different (i.e., the synthesis is easier and less expensive). Propargyl terminated sulfone monomers and resins therefrom have also been disclosed. See. U.S. Pat. No. 4,226,800 to Picklesimer. Once again, the chemistry involved is entirely different; propargyl (HC.tbd.C--CH.sub.2 --) groups are used to introduce cross-linking versus the ethynyl and substituted ethynyl groups (--C.tbd.C--X), employed in the present invention. The polymers in Picklesimer are thermosets, whereas the polymers of the present invention, depending on the molecular weight of the precursor polysulfone, are thermoplastics. Thermosets are generally high strength, brittle materials with low impact strength. Thermoplastics are relatively high strength, tough materials with high impact strength. Furthermore, thermosets cannot be reformed once they have cured whereas thermoplastics can be reformed as necessary. This feature makes thermoplastics commercially more attractive because scraps and faulted moldings can be reprocessed, thus reducing waste. There is thus a definite need in the art for a thermoplastic polysulfone exhibiting improved resistance to solvents and creep at elevated temperatures.
Accordingly, it is an object of this invention to provide a new thermoplastic composition produced from polysulfones and containing various degrees of cross-linking.
Another object of the present invention is to provide a new thermoplastic composition that will chain extend upon curing.
It is yet another object of the present invention to provide novel thermoplastic polysulfones which exhibit improved use temperatures and solvent resistance.
It is a further object of the present invention to provide a high yield process for preparing thermoplastic polysulfones which exhibit improved use temperatures and solvent resistance.